HeterobasidionRoot Disease Efforts to delimit the occurrence of Heterobasidion root disease (HRD) continued in 2012. Surveys were concentrated in the northwest Lower Peninsula in the region where HRD was confirmed in 2011. Numerous pockets of pine mortality in actively managed plantations were surveyed this year. No new infections of HRD were confirmed.
Unlike many forest insects and diseases that are attracted to stands stressed by lack of management, HRD is most commonly found in actively managed forest stands.
In Michigan, red pine, jack pine and white pine are most susceptible. Fresh cut stumps provide an ideal entry path for spores of HRD, which move through grafted roots to infect healthy trees. Infected trees suffer from thinned crowns and reduced height, diameter and shoot growth. Over time, circular pockets of dead and dying trees mark the progression of the disease.
Caused by the fungus Heterobasidion irregularae (formerly Heterobasidion annosum), this disease is considered among the most destructive fungi in North American forests. Effective control measures for HRD have been developed. Fungicides applied to freshly cut stumps prevent HRD from entering and moving to healthy trees through the root system. This approach, while effective, would pose additional costs and restrictions on the harvest of Michigan’s pine resources.
With the discovery of an active HRD infection in Wexford County in 2011, and with HRD being established across much of our neighboring state Wisconsin, early identification and containment of HRD in Michigan has become a forest health priority.
In 2013 the Department of Natural Resources will work with Michigan Technological University to conduct statewide surveys to delimit the presence and distribution of HRD in Michigan. Intensified identification of pockets of pine mortality through routine inventory and by aerial survey will be important in developing an adequate pool of potential HRD sites to aid in this statewide survey.